Which cycle is primarily stored in the atmosphere but cannot be used in its atmospheric form?

The nitrogen cycle is the process that centers around the transformations of nitrogen in various chemical forms, including its presence in the atmosphere. Nitrogen makes up a significant portion of the Earth's atmosphere in the form of nitrogen gas (N2), which is abundant but not usable directly by most living organisms.

For organisms, particularly plants and animals, nitrogen must be converted into forms that they can utilize, such as ammonia (NH3) or nitrates (NO3-). This conversion process involves several key steps including nitrogen fixation, nitrification, and denitrification, carried out by various bacteria in the soil and water. These bacteria facilitate the transformation of atmospheric nitrogen into usable forms, thus making it crucial for life.

In contrast, while the water cycle involves processes that are vital for life and is stored in various forms in the atmosphere, water in its gaseous state (water vapor) is readily usable once it condenses into liquid. The carbon cycle involves carbon dioxide in the atmosphere that plants can utilize through photosynthesis, and the phosphorus cycle, while important for living organisms, does not have a significant atmospheric component.

Thus, the nitrogen cycle is unique in that the most prevalent form of nitrogen found in the atmosphere is not suitable for direct uptake by living